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Introduction to Heliophysics and the 2013 Decadal Survey

1.1 HELIOPHYSICS SCIENCE INTRODUCTION

Heliophysics is the study of our star, the Sun, its influences on the planets of our solar system, and its interaction with interstellar space (Figure 1.1). The region of space influenced by the Sun, called the heliosphere, extends past Pluto’s orbit into the local interstellar medium. Filled with plasma (ionized gas) and neutrals (non-ionized gas) and threaded by the magnetic fields of the Sun and the magnetized planets, the heliosphere and the planetary atmospheres within provide a rich laboratory for studying neutral and plasma processes, dynamics (waves), and interactions that occur throughout the universe. Heliophysics is a discovery science that is deeply connected to questions of life and habitability and thus embodies fundamental questions about the origin and fate of habitable planetary environments. The influence of these processes is increasingly important here on Earth as our society becomes more dependent on technologies that are impacted by space weather. This important aspect of heliophysics research focuses on understanding the science behind the solar and lower-atmosphere influences on Earth’s upper atmosphere, the near-Earth space environment, and the space weather effects that can disrupt our satellite, communication, navigation, and power grid technologies. A number of resources are available to learn more about the field of heliophysics (Box 1.1).

As shown in Figure 1.1a, the Sun consists of several layers: an inner core, the surrounding convection zone, the photosphere that is its visible surface, and its highly ionized atmosphere, which ultimately becomes the solar wind. The solar wind plasma reaches supersonic speeds at a distance of a few solar radii from the Sun. From there, the solar wind carries its energy and momentum through interplanetary space, interacting with the magnetic fields, atmospheres, or surfaces of solar system bodies along the way.

Earth’s extended magnetic field in space, known as the magnetosphere, is shaped by the solar wind, which compresses Earth’s intrinsic dipole magnetic field on its sunward side and elongates it on the night-side to produce the magnetotail. Earth’s upper atmosphere, consisting of the ionosphere, thermosphere, and mesosphere at about 50-500 km above ground, makes up the inner boundary of the magnetosphere. The ionosphere, thermosphere, and mesosphere serve as the critical link between external particle and energy inputs related to the solar wind interaction with the magnetosphere and the lower atmosphere from which waves generated in the troposphere near Earth’s surface have propagated upward (Figure 1.1b). At

the same time, the thermosphere acts as a natural thermostat for Earth’s upper atmosphere by radiating away excess energy received from the Sun into space.

The ionosphere and thermosphere are also sources of magnetospheric material and are a load on the solar wind “driving” of the coupled magnetosphere-ionosphere-thermosphere system. Magnetic storms and auroral activity, including their effects on the radiation belts and ionosphere, are some of the more widely known aspects of the highly variable solar wind-magnetosphere interaction. Chains of heliophysics processes are involved in producing such outcomes, including complex physical couplings of the already complex subsystems that make up our natural environment in space.

At the furthest reaches of the heliosphere, the distant solar wind mingles with interstellar gas and dust before coming to a stop at a boundary called the heliopause (Figure 1.1c). Recently, Voyager 2, a NASA spacecraft launched in 1977 that flew by Jupiter and Saturn before becoming the first (and only) spacecraft to fly by Uranus and Neptune, crossed this boundary, more than 18 billion km from Earth. Here galactic cosmic rays are both entering the heliosphere from outside the solar system and being energized by ambient particle populations. These highly energetic cosmic rays have important space weather implications for exploration beyond our home planet.

1.2 FUNDAMENTAL PHYSICAL PROCESSES IN HELIOPHYSICS

Heliophysics research provides an opportunity to explore fundamental plasma processes that also have important applications in laboratory plasma physics and for other astrophysical systems. Six fundamental, universal processes were discussed in Solar and Space Physics: A Science for a Technological Society (NRC, 2013), the second National Academies of Sciences, Engineering, and Medicine decadal survey in solar and space physics, or heliophysics (hereafter the 2013 decadal survey)—as listed in Table 1.1: dynamos, magnetic reconnection, solar and planetary winds, collisionless shocks, turbulence, and plasma-neutral interactions. Each of these is briefly described in this section, and a few examples of recent research results are highlighted in Chapter 2 to further elucidate some of these fundamental processes.

Dynamos

The level of solar activity is primarily due to the Sun’s response to its internal dynamo cycles. The dynamo produces complex patterns of magnetic fields, including sunspots, that both structure the Sun’s corona and solar wind, and lead to flaring and the eruptive activity called coronal mass ejections (CMEs)—giant transient expulsions of plasma and magnetic field that drive energetic particle-producing interplanetary shock waves. Dynamos are also active in other stars, producing star spots and stellar activity that influences the space environments of exoplanets. The first observation of a CME from another star was recently made with the Chandra X-ray Observatory (Argiroffi et al., 2019).

Uncovering how internal solar couplings drive dynamo cycles and how that dynamo leads to the phenomena at the solar surface are among the most challenging problems in heliophysics. The dynamo occurs deep within the Sun, hidden from direct observation. The tool of helioseismology provides access to some of the deep large-scale flows involved, but even this powerful diagnostic cannot probe the relatively small scale of convective motions, and helioseismology has not yet been able to measure the slow circulation known as the “meridional flow” at depth considered essential in transporting magnetic field across latitude. The solar dynamo problem requires an intrinsically multidisciplinary approach: development of a comprehensive, first-principles numerical model of the solar dynamo that (1) requires sustained investment in state-of-the-art computational means, (2) will benefit from the development of multi-perspective long-term helioseismology, and (3) needs multiyear observations of a substantial sample of Sun-like stars to test

and validate the forecast capability of any dynamo model within years rather than the decades needed if only the Sun were used.

Earth’s ionosphere exhibits several neutral wind dynamo processes that at high latitudes generate large-scale electric fields that affect the magnetosphere. Electric fields generated at low latitudes through the wave-driven E-region dynamo are the primary mechanism by which meteorological weather at the surface, such as El Niño, is imprinted upon the space weather of the ionosphere and thermosphere, leading to very large variations in plasma densities generated by solar radiation. The same dynamo-driven waves are fundamental to all planetary atmospheres, especially so for planets with strong magnetic fields like Jupiter, thus heliophysics research results are important for comparative planetary studies (Bagenal, 2013). For example, these waves are very prominent on Mars as observed by the Mars Reconnaissance Orbiter (MRO) and Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. Significant challenges to understanding neutral wind dynamo effects exist—for one, single satellites inherently lack the local time resolution to resolve the ionospheric imprints of day-to-day weather variability. The neutral wind dynamo problem requires a suite of complementary electric field, plasma, and neutral wind measurements from multi-point spatial and local time perspectives, which only constellations can provide, to constrain models and to close the loop on the weather-space weather connection.

Solar and Planetary Winds

Ion and electron “winds” or outflows occur from both stars, including our Sun, as well as from planets with significant atmospheres. These winds can be driven by radiative heating at the base of the atmosphere, which can even cause neutral gas to participate. Other means of energy transfer involving often multi-stage, complicated processes are also possible. The solar wind was originally conceived as an exosphere-like expansion of the heated, mainly ionized hydrogen corona into the heliosphere. However, even the earliest observations of solar wind in the 1960s indicated that much of its behavior is fluid-like, and that magnetohydrodynamic (MHD) and plasma waves are involved in both its initial creation as well as its heliospheric evolution. In addition, the Sun’s structured coronal source regions produce streams of

TABLE 1.1 Six Universal Processes as listed in 2013 Solar and Space Physics (Heliophysics) Decadal Survey

Universal Process		Description
	Dynamos	Process that creates and transports magnetic field. Important for 11-year solar activity cycle, generation of electric field in Earth’s polar regions, and magnetic activity in stars and galaxies.
	Solar and Planetary Winds	Process of heating and ejecting particles from an atmosphere. Important for the solar wind, Earth’s ionosphere wind into the magnetosphere, and stellar wind.
	Magnetic Reconnection	Process of magnetic field of opposite direction annihilating each other to explosively convert magnetic energy into heat, radiation, and energetic particles. Important for solar flares, coronal mass ejections, driver for substorms in Earth’s magnetosphere, stellar flares, and astrophysical jets.
	Collisionless Shocks	Shock waves are formed in the transition from supersonic to subsonic flow, which then heats the plasma and accelerate particles. Important for planetary bow shocks, interplanetary shock waves, supernova shocks, and galaxy collisions.
	Turbulence	Process of plasma interaction that heats the plasma and accelerates particles. Important for heating the solar corona, driving plasma transport in Earth’s magnetosphere, and facilitating accretion disk formation around stars and planets.
	Plasma-Neutral Interactions	Process of ionized plasma (charged) and neutral particles (uncharged) interacting to increase ionization and direct outflows. Important for heating in the solar chromosphere, enhanced ionization in Earth’s ionosphere/thermosphere, interaction of solar wind with the interstellar medium, planetary atmospheric escape, and structuring in astrophysical molecular clouds.

SOURCE: Figures (top to bottom) from https://figshare.com/articles/Schematic_of_the_Solar_Dynamo/102094, courtesy of Paul Higgins; https://pwg.gsfc.nasa.gov/istp/outreach/images/Gusts/windsprl.jpg, courtesy of NASA Goddard Space Flight Center; https://mms.gsfc.nasa.gov/images/science_page/science_1_lg.png, courtesy of NASA Goddard Space Flight Center; https://www.bu.edu/blazars/BLLac.html, courtesy of Wolfgang Steffen, UNAM; https://svs.gsfc.nasa.gov/vis/a010000/a012900/a012901/MMS_Poster_Turbulence_v8_Cropped.jpeg, courtesy of NASA Goddard Space Flight Center/Mary Pat Hrybyk-Keith; see R. J. Lillis, D.A. Brain, S.W. Bougher, F. Leblanc, J.G. Luhmann, B.M. Jakosky, R. Modolo, et al., Characterizing Atmospheric Escape from Mars Today and Through Time, with MAVEN, Space Science Reviews 195:357-422, courtesy of S. Bartlett and D. Brain.

different speeds, densities, and compositions that interact as they move outward from the rotating Sun. Transient variations in the solar magnetic field significantly affect the solar wind in the ecliptic plane over a wide range of temporal and spatial scales. During times of high solar activity, the solar wind can be dominated by transient outflows, including the massive outbursts—CMEs. Thus, there is a variety of solar wind behaviors whose physical underpinnings continue to challenge researchers, even as new observations and physics-based modeling allow us to better understand the underlying processes. Meanwhile, inferring stellar wind properties of other stars from much more limited observational information is still in its infancy.

By contrast, the light gases escaping from a planet’s atmosphere, also known as planetary winds, are much more quiescent outflows but are potentially key to understanding to what extent, and how, the Sun transfers energy to planetary atmospheres via nonradiative processes. While planetary upper atmospheric gases, especially lighter species, can escape via atmospheric expansion due to thermal pressure gradients, observations (especially at Earth) show that other processes also energize heavier ions in the upper atmosphere at high latitudes, leading to heavy ion outflows. These ion winds can affect the magnetosphere by providing a source of heavy ions that influence its response to both external driving by the solar wind interaction and its internal dynamics. For example, on Earth, waves caused by auroral precipitation or solar wind energizes oxygen ions in the high latitudes. Oxygen ions are driven upward by diverging magnetic fields, where they can escape and populate the outer magnetosphere. These ions then become a major component of the geomagnetic storm ring current. In planetary settings where a magnetosphere is weak or absent, similar energized ion outflows occur. In all cases, they contribute to the loss of atmospheric gases over time, with possible profound effects on geological time scales. Required for these winds are processes that can accelerate the charged particles to be faster than the escape velocity, which is about 10 km/s for Earth and about 600 km/s for the Sun. Both experimental and theoretical research continues to provide new insights into these diverse ion wind-generating settings.

Magnetic Reconnection

The generation and evolution of the magnetic field of the Sun is driven by its dynamo, but magnetic reconnection is the process that causes explosive events. During magnetic reconnection, magnetic fields embedded in a plasma change their topology and, in the process, release enormous amounts of energy. Reconnection is the fundamental process responsible for solar flares and CMEs, for the dynamic coupling of the solar wind to the near-Earth space environment, and the ultimate driver for space weather. It is also thought to be responsible for many explosive phenomena in astrophysical plasma environments, such as acceleration of astrophysical jets, pulsars, and possibly gamma-ray bursts and cosmic ray acceleration (e.g., Lazarian et al., 2014; Zweibel and Yamada, 2009). On Earth, understanding magnetic reconnection is critical for realizing successful magnetic confinement schemes for energy-producing fusion devices. However, the scale of laboratory plasmas is too small to make detailed measurements of magnetic reconnection. Only in space can we probe the region where magnetic reconnection occurs. The near-Earth environment is the only practical place in the solar system where we can study the microphysics of this universal process.

Another area of broad interest, particle acceleration, is ubiquitous throughout the universe. Close to home, on the Sun and in Earth’s and other planetary radiation belts, we can learn how particles get accelerated to ultra-relativistic energies. In fact, some 50 percent of the energy released during a solar flare magnetic reconnection event goes into the acceleration of particles. In ground-level-events (GLEs), giga-electron-volt protons generated near the Sun in connection with some fast CMEs produce secondary radiation signatures in distributed neutron monitor networks over wide swaths of Earth’s surface. Both shocks in the plasmas and reconnection are possible contributors. Understanding these processes may shed light on particle acceleration in other corners of the universe such as in black holes and pulsars.

Collisionless Shocks

Shocks are formed when the relative speed of an object in a medium is faster than the sound speed of the medium. For example, in a neutral fluid, any disturbance, like that produced by a flying plane, causes a compression of air—a sound wave—to propagate in the medium. When the speed of the plane reaches the sound speed and becomes supersonic, it overtakes the compression wave front resulting in rapid change of state—a shock, which can be heard as a sonic boom. The upstream and downstream properties of the fluid through the shock are different, and the state of the downstream fluid is not constant but continuously changes to reach the new equilibrium state. In neutral fluids, the thickness of the shock is determined by the distance between collisions of the fluid particles.

There are fundamental differences between shocks in neutral fluids and in magnetized plasmas such as the solar wind or interstellar medium. The planetary bow shock that forms in front of magnetized planets is an example of a collisionless shock, where the thickness of the shock is much less than the distance between collisions of the plasma particles. Instead of collisions, the particles at collisionless shocks communicate by electromagnetic fields. These interactions are fundamentally responsible for the deceleration, compression, and heating of the magnetized plasma downstream of the shock.

Interplanetary shock waves arise due to CMEs moving faster than the surrounding medium (i.e., the solar wind) by more than the sound speed. Various wave-particle interactions in the shocked region of the CME accelerate the particles. Due to their common occurrence in the universe, collisionless shocks can be considered as universal particle accelerators. For example, they occur in the interstellar medium when a star reaches the end of its life cycle and explodes as a supernova as well as in the accretion process at the edge of galaxy clusters. These shocks are responsible for the generation of extremely energetic particles, galactic cosmic rays (GCRs), which can reach Earth more easily during the solar minimum when the Sun’s magnetic field offers less protection. Recent heliophysics missions (e.g., NASA’s THEMIS and MMS or the European Space Agency’s Cluster) have made it possible to probe the bow shock with in situ, multi-point measurements. Such measurements help us better understand the shock structure and physics responsible for particle acceleration processes during varying solar wind conditions and space weather events. Understanding shock-driven acceleration processes from a basic physics perspective is essential for the better prediction of the energetic particle environment and for keeping technological societies safe at Earth, and eventually perhaps the Moon, Mars, and beyond.

Turbulence and Instabilities

Another fundamental process in heliophysics is related to plasma turbulence, instabilities, and associated cross-field transport. These are also critical topics for building more stable laboratory plasma experiments and fusion devices. For example, one advance for steady-state operation of a tokamak fusion device is suppression of the plasma instabilities near the plasma boundary by introducing small-scale magnetic ripples that disrupt the formation of larger-scale instabilities (Nazikian et al., 2018). Further investigations of natural plasma turbulence in the solar wind and in Earth’s magnetosphere could provide important input to these laboratory problems. Furthermore, the key roles of turbulence in Jupiter’s vast magnetosphere, as learned from NASA’s Juno mission (Clark et al., 2018), are applicable for comparison to solar atmosphere turbulence.

The stability of an environment determines if small perturbations are damped out or grow to large amplitudes. Plasma instabilities can grow due to sources of free-energy in the system. Turbulence is ubiquitous in the ionosphere where it is largely driven by atmospheric waves that are themselves a universal process in planetary atmospheres. In the heliosphere, free-energy sources are ubiquitous including, for example, magnetic shear, velocity shear, and gravity acting on a density gradient. Velocity shear–driven Kelvin-Helmholtz

instability (KHI) has been observed at the magnetopause/ionopause of most planets in the solar system and can lead to the formation of flow vortices and the onset of turbulence. Secondary instabilities and processes (e.g., magnetic reconnection) can occur within these vortices, which can lead to plasma transport. Small-scale turbulence and wave-particle interactions are important for plasma heating and producing anomalous resistivity, which can lead to violation of frozen-in conditions in collisionless reconnection. In the ionosphere, electrons heated by electrojet turbulence lower the electric potential across the polar-cap and thus impact magnetosphere-ionosphere coupling, such as increasing the peak pressure in the inner magnetosphere. Thus local, small-scale processes can have global implications that affect the entire magnetosphere.

Plasma-Neutral Interactions

Plasma-neutral interactions can be thought of as a unique physics domain present throughout the Sun’s heliosphere, where neutral particles and charged particles collisionally interact in a manner that influences the behavior and structure of both neutral and plasma states. These interactions produce phenomena and variability unique to this environment. In our solar system, plasma-neutral interactions exist within the ionosphere-thermosphere-mesosphere (ITM) regions of planetary atmospheres and also at the boundary of the solar system with the local interstellar medium, and within the solar chromosphere and prominences, where transitions between strongly neutral and strongly ionized plasma in magnetic environments are common. There is also important plasma-neutral interactions at a larger scale with the moons embedded in Jupiter’s vast magnetosphere. An even broader net is cast in astrophysics, where plasma-neutral interactions play a key role in defining protostellar discs, galactic molecular clouds, exoplanet atmospheres, stellar atmospheres, and dusty plasmas of comets (Ballester et al., 2018).

Plasma-neutral interactions in planetary systems occur in the transition region where outer space interacts with the gaseous envelope of the planet, forming an energy terminus in the chain of stellar-planetary interactions. This energy terminus forms the basis of “space weather” in Earth’s geospace system with plasma-neutral interactions playing a critical role in spawning ITM variability that continues to limit predictability and plague our space assets. That one of the most complex examples of plasma-neutral interactions—Earth’s ITM—is readily accessible to all modern research tools for investigation offers an extraordinary opportunity not only to advance understanding of Earth, but to expand knowledge of the nature of plasma-neutral interactions everywhere.

For objects with dense gases at their visible surface (the Sun, stars, the giant planets of our solar system, and exoplanets), investigation of variability in their weakly or partially ionized environments (i.e., regions within which plasma-neutral interactions are operative) includes direct ion-neutral momentum coupling, photochemistry between both neutrals and ions, and plasma transport. A further complex source of variability occurs for worlds where surface topology modulates upwardly directed–wave energy and transfers that energy by coupling from neutrals to plasmas. Earth, Venus, Mars, and Titan are specific examples of this additional complexity. Further complexities occur in the presence of a strong intrinsic geomagnetic field that communicates distant and disparate fields and waves from the plasma to the neutral gas through plasma-neutral interactions; Earth, Saturn, and Jupiter are examples of planets whose upper atmospheres are magnetically influenced in this way, as are stellar atmospheres.

These six fundamental, universal processes are examples of the many complex processes important in understanding heliophysics. Rarely is a single process the only key process; instead, the different processes are in play all the time, and features of a specific process can be revealed more clearly during specific events or with specialized instrumentation or observational configurations (e.g., multiple views of the same observation). The complexity of interacting processes requires a system-level approach for many of the research topics in heliophysics. A few of these research topics are further discussed in Chapter 2.

1.3 CURRENT HELIOPHYSICS MISSIONS AND MAJOR PROGRAMS

Heliophysics research is broadly supported by NASA’s Heliophysics Science Division, NSF’s Geospace Section of its Division of Atmospheric and Geospace Sciences (AGS), and NSF’s Division of Astronomical Sciences (AST). Space weather, which is often considered an applied part of heliophysics, is supported by those science divisions as well as space weather operations that are led by the NOAA Space Weather Prediction Center (SWPC) and Air Force Weather Agency (AFWA). Furthermore, the National Space Weather Program (NSWP) has facilitated collaborations between 10 federal agencies, industry, and the academic community to provide improvements in the capabilities of space weather services (Bonadonna et al., 2017). The current NASA and NOAA missions and NSF major facilities and programs are summarized here to provide context on the resources needed for heliophysics research and space weather operations.

There are currently 19 NASA research missions, encompassing 26 spacecraft, that are operating as of October 2019 (see Figure 1.2 and Table 1.2), and there are 5 missions being prepared for launch in the next 5 years. Strategic missions are funded through the Solar-Terrestrial Probes (STP) Program, which focuses on fundamental physical processes, and the Living With a Star (LWS) program, which focuses on those aspects of heliophysics science that may affect life and society. Smaller missions are developed as part of the Explorers program, which includes Medium-Class Explorers (MIDEX), Small Explorers (SMEX), and Missions of Opportunity (MoOs). NASA Heliophysics Division also has dozens of CubeSats, rockets, and balloon experiments that are not included in the Table 1.2 list.

In addition to missions, NASA has research programs for data analysis, theory, and computational studies. The majority of these are program elements of the annual ROSES (Research Opportunities in Earth and Space Science) call. Examples include Heliophysics Guest Investigator (HGI), Heliophysics Supporting Research (HSR), Heliophysics Theory, Modeling and Simulations, LWS Science, and Heliophysics Technology and Instrument Development for Science (H-TIDeS) program elements. These programs play a vital part in addressing NASA’s Heliophysics science goals and maximizing the science return from the Heliophysics missions.

There are currently 19 NSF facilities and programs operating as listed in Table 1.3. Many of these facilities and laboratories have been in operation for decades. The more recent observatory developments include the Atacama Large Millimeter Array (ALMA), Low-latitude Ionospheric Sensor Network (LISN), Expanded Owens Valley Solar Array (EOVSA), and Daniel K. Inouye Solar Telescope (DKIST). NSF facility investments have been shifting toward distributed facility concepts, often involving cost-effective opportunistic networks (e.g., Global Positioning System [GPS], SuperMAG, and Active Magnetosphere and Planetary Electrodynamics Response Experiment [AMPERE]), as illustrated in Figure 1.3. NSF supports scientific research through its open grant program and focused-topic grants through Geospace Environment Modeling (GEM), Coupling, Energetics and Dynamics of Atmospheric Regions (CEDAR), and Solar Heliospheric and Interplanetary Environment (SHINE). NSF also supports annual GEM/CEDAR/SHINE workshops that enable community organization and collaboration and have a significant educational impact. For example, in 2018, 73 graduate students attended GEM, 68 of whom received full support from NSF to attend the meeting.¹

Although the NSWP is spread across 10 federal agencies, the midterm assessment committee focus is on the agencies that conduct space weather research and whose roles in the NSWP were examined by the decadal survey committee: NASA, NSF, and NOAA. The key NOAA space weather observations include their Geostationary Operational Environmental Satellites (GOES) series in GEO, the Space Environment Monitor on NOAA Polar-Orbiting Operational Environmental Satellite polar satellites, and the Deep Space Climate Observatory (DSCOVR) at the Lagrange point 1 (L1) location. NOAA also supports space weather observations from the NSF GONG ground network for solar magnetic fields and the NASA ACE satellite for L1 solar wind data. NOAA has a future Space Weather Follow-On mission planned for L1 with a launch in Fall 2024 with NASA’s IMAP mission. NOAA is also considering space weather operations at L5 (east view of Sun) with potential partners of ESA and NASA. In addition, NOAA’s COSMIC-2 (Constellation Observing System for Meteorology, Ionosphere, and Climate) with its six-satellite constellation for radio occulation measurements provides space weather products about the total electron content in Earth’s ionosphere.

1.4 HIGHLIGHTS OF THE 2013 SOLAR AND SPACE PHYSICS (HELIOPHYSICS) DECADAL SURVEY RECOMMENDATIONS

The 2013 decadal survey (NRC, 2013) recommended a comprehensive program of research organized around four key science goals:

Key Science Goal 1. Determine the origins of the Sun’s activity and predict the variations in the space environment.

Key Science Goal 2. Determine the dynamics and coupling of Earth’s magnetosphere, ionosphere, and atmosphere and their response to solar and terrestrial inputs.

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¹ Data taken from the GEMStone Newsletter, Volume 29, Number 1, January 2019, http://spc.igpp.ucla.edu/gem/GEMstone/GEMstone_Vol29_No1.pdf.

TABLE 1.2 List of NASA Heliophysics Missions Currently Operating in 2019

NOTE: Four (4) are in prime mission (in green highlight), and 15 missions are extended. There was a period in 2017-2018 when there were no prime missions for NASA Heliophysics Division. Acronyms are defined in Appendix F.

Key Science Goal 3. Determine the interaction of the Sun with the solar system and the interstellar medium.

Key Science Goal 4. Discover and characterize fundamental processes that occur both within the heliosphere and throughout the universe. (p. 3)

Flowing from these goals were science challenges and objectives (NRC, 2013, Chapter 2). To fulfill the objectives of the decadal survey, the survey committee made 20 top-level next-decade recommendations for NASA, NSF, and NOAA heliophysics and space weather programs. These are shown in Table 1.4; they are the focus for this midterm assessment.

The decadal survey committee included a top-level steering committee and three science discipline panels (also referred to as study panels): Atmosphere-Ionosphere- Magnetosphere Interactions, Solar Wind-Magnetosphere Interactions, and Solar and Heliospheric Physics. It also included five working groups that examined crosscutting areas: Theory, Modeling, and Data Exploitation; Explorers, Suborbital, and Other Platforms; Innovations: Technology, Instruments, and Data Systems; Research to Operations/Operations to Research; and Education and Workforce.

The science discipline panels specified a number of science objectives that steered the decadal survey top-level goals and recommendations. These disciplinary panels also defined 12 top-level science challenges organized by the three disciplines. This midterm assessment committee view of the relationship of these 12 challenges to the key science goals is presented below in Chapter 2 and its Table 2.1.

1.5 MIDTERM ASSESSMENT COMMITTEE CHARGE AND REPORT OUTLINE

The midterm assessment committee was convened by the Space Studies Board of the National Academies of Sciences, Engineering, and Medicine in December 2018 to address seven tasks—listed in Table 1.5, which also lists findings from this committee that are mapped to subsequent chapters in this report. It should also be noted that in addition to the present midterm assessment, there are other recent reviews of NASA and NSF solar and space physics programs (Box 1.2).

This report is organized into six chapters plus a Summary. Chapter 1 (this chapter) provides a brief description of the field of heliophysics and current heliophysics programs at relevant federal agencies. In Chapter 2, a few science highlights in each of the three heliophysics subdisciplines are described to provide a flavor for some of the exciting science accomplishments already realized during the first part of the decade (2013-2019). Chapter 3 provides a more detailed assessment of progress towards each of the research recommendations made in the 2013 decadal survey, as well as identifying challenges and opportunities for the remainder of the current decade. Similarly, Chapter 4 discusses the recent progress and near future opportunities for the application recommendations in the 2013 decadal survey. Consideration of ways to further enhance and develop a strong and diverse workforce in order to maximize progress in the coming decades is discussed in Chapter 5. Chapter 6 discusses planning that could be undertaken during the remainder of the decade in preparation for the next decadal survey, which is expected to start in 2022.

TABLE 1.3 Major National Science Foundation (NSF) Facilities/Programs

NOTE: Facility names in green are NSF Division of Atmospheric and Geospace Sciences facilities. Facility names in red are NSF Division of Astronomical Sciences facilities. This list is sorted by start date. Acronyms are defined in Appendix F.

TABLE 1.4 The 20 Top-Level Recommendations from the 2013 Solar and Space Physics (Heliophysics) Decadal Survey

NOTE: Acronyms defined in Appendix F.

TABLE 1.5 Tasks for the Solar and Space Physics (Heliophysics) Decadal Survey Midterm Assessment Committee

1.6 REFERENCES